Hyperbranched Photo Responsive and Liquid Crystalline Azo-Siloxane Polymers Synthesized by Click Chemistry Someshwarnath Pandey, Sarada P. Mishra, Balakrishna Kolli, Tapan Kanai, Asit B. Samui Polymer Science and Technology Centre, Naval Materials Research Laboratory, Shil-Badlapur Road, Ambernath 421506, Maharashtra, India Correspondence to: A. B. Samui (E-mail: absamui@gmail.com) Received 14 February 2012; accepted 8 March 2012; published online 30 March 2012 DOI: 10.1002/pola.26042 ABSTRACT: Three new types of hyperbranched photoactive liq- uid crystalline siloxane polymers containing azo moieties were synthesized using click chemistry methodology. The polymers were soluble in most of the polar solvents like chloroform, tet- rahydrofuran, dimethylformamide, dimethyl sulphoxide and dichloromethane. The molecular weights of the polymers were in the range of 9000–12,000 g mol 1 . The trans-cis photoisome- rization of the polymer were studied both under UV radiation and dark. The isomerization rate constants were found to be in the range of 0.7–1.4  10 2 sec 1 and 7.0 2.5  10 5 sec 1 . The thermotropic behavior of the polymers was studied by using polarizing optical microscopy and differential scanning calorimetry, respectively. The polymers P1 and P2 showed liq- uid crystalline texture characteristic of nematic phase. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 2659–2668, 2012 KEYWORDS: azo polymers; click chemistry; hyperbranched; liquid crystalline; liquid-crystalline polymers (LCP); nematic; photo- chemistry; photoswitching; polysiloxanes; UV–vis spectroscopy INTRODUCTION A very active research field is represented by the studies on azobenzene containing liquid crystalline polymers. 1–4 The reversible trans-cis photoisomerization of the azo-benzene can be utilized to design new advanced materials coupled with understanding of new phenomenon and its underlying mechanisms. The resulting materials have wide range of applications such as optical data storage and other device applications. 1–7 A recent discovery by Ikeda and coworkers illustrates the light directed bending and unbend- ing of thin films of crosslinked azobenzene liquid crystalline polymer which can be used as an actuator for microdevice applications. 8 Surface relief grating (SRG) is an example reported by two groups independently in 1995. 9,10 Recently, azo polymers are being synthesized with diverse architec- tures such as dendrimers, 11 proteins, 12 micelles, 13 and sol- gel materials 14 for studying the photoactivity directed applications. In our earlier work linear siloxane polymers having azo side group have been synthesized and characterized. 15 The poly- mers were observed to undergo tran-cis isomerization at a very high rate. The polymers were further analyzed for their photomechanical properties. The rate was found to be quite encouraging. Encouraged by the result, further study was planned by synthesizing hyperbranched polymers containing both siloxane and azo moieties. A good number of reports are available in literature on hyperbranched polymer in general and photoactive polymer in particular. Synthesis and charac- terization of branched LC polymers containing disc like meso- gens 16 and rod-like mesogens based on conformational iso- merism 17,18 were reported for the first time by Percec et al. The electrophilic cyclotetramerization polymerization of 3,4-bis(n-alkyloxy) benzyl alcohol with an a,x-bis{[2-(alkoxy)- 5-(hydroxymethyl)phenyl]oxy} alkane 16 resulted in hyper- branched polymer with cyclotetraveratrylene units in the branching points. Synthesis of hyperbranched 10-bromo-1- (4-hydroxy-4 0 -biphenylyl)-2-(4-hydroxyphenyl) decane (TPD- b) based polymers demonstrating the dependence of phase behavior on the nature of their chain end was also reported. 17 Synthesis of dendrons up to fourth generation and their phase behavior study were also reported. 19 Viscoelastic properties of dilute nematic mixtures containing cyclic and hyper- branched liquid crystalline polymers dissolved in a nematic solvent were studied. 20 Rational design for the first nonspher- ical dendrimers showing calamitic nematic and smectic phases was reported by Percec et al. 21 The dramatic stabiliza- tion of hexagonal columnar mesophase was generated from supramolecular and macromolecular columns, respectively. 22 Design of first spherical supramolecular dendrimers which self organize into cubic LC phase 23 and controlling polymer shape through self assembly of dendritic side group 24 appeared in quick succession. The individual spherical and cy- lindrical supramolecular dendrimers started getting confirmed V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2659–2668 2659 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE